U.S. patent application number 10/269172 was filed with the patent office on 2003-02-13 for package structure for mounting a field emitting device in an electron gun.
Invention is credited to Kalar, Kent R., Kloba, Anthony A., Schueller, Randolph D..
Application Number | 20030032362 10/269172 |
Document ID | / |
Family ID | 23959989 |
Filed Date | 2003-02-13 |
United States Patent
Application |
20030032362 |
Kind Code |
A1 |
Schueller, Randolph D. ; et
al. |
February 13, 2003 |
Package structure for mounting a field emitting device in an
electron gun
Abstract
Apparatus and method are provided for a package structure that
enables mounting of a field-emitting cathode into an electron gun.
A non-conducting substrate has the cathode attached and the cathode
is electrically connected to a pin through the substrate. Other
pins are electrically connected to electrodes integral with the
cathode. Three cathodes may be mounted on a die flag region to form
an electron gun suitable for color CRTs. Accurate alignment of an
emitter array to the apertures in the electron gun and other
electrodes such as a focusing lens is achieved. The single package
design may be used for many gun sizes. Assembly and attachment of
the emitter array to the electron gun during construction of the
gun can lower cost of construction.
Inventors: |
Schueller, Randolph D.;
(Austin, TX) ; Kalar, Kent R.; (Austin, TX)
; Kloba, Anthony A.; (Austin, TX) |
Correspondence
Address: |
Michael A. Hawes
Baker Botts L.L.P.
One shell Plaza
910 Louisiana Street
Houston
TX
77002-4995
US
|
Family ID: |
23959989 |
Appl. No.: |
10/269172 |
Filed: |
October 11, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10269172 |
Oct 11, 2002 |
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09493379 |
Jan 28, 2000 |
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6469433 |
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Current U.S.
Class: |
445/50 |
Current CPC
Class: |
H01J 29/485 20130101;
H01J 2201/304 20130101; H01J 29/481 20130101; H01J 3/021
20130101 |
Class at
Publication: |
445/50 |
International
Class: |
H01J 009/04 |
Claims
What we claim is:
1. A method for making a field-emitting cathode assembly,
comprising: providing a non-conductive substrate, the substrate
having a first and a second surface, and a first conductive pin
electrically connected to the first surface and extending from the
second surface providing a field-emitting device having an emitting
array and attaching the device to the first surface and
electrically connecting the device to the first conductive pin;
electrically connecting at least one electrode of the
field-emitting device to a second conductive pin, the second
conductive pin extending from the second surface; providing an
alignment member having a least one aperture therein and a selected
diameter; providing a spacer to place the alignment member at a
selected distance from the substrate; and joining the substrate and
alignment member at a selected spaced-apart distance.
2. The method of claim 1 wherein the method of joining is selected
from the methods of welding, brazing and applying adhesive.
3. The method of claim 1 wherein the alignment member is a disk and
the disk further comprises a cylindrical side therein.
4. The method of claim 1 wherein the alignment member is a can.
5. A method for assembling an electron gun, comprising: providing a
field-emitting cathode assembly having an alignment member, the
alignment member having at least one aperture and a selected
diameter; providing a lens to be a part of the electron gun, the
lens having an aperture; providing an aligning tool adapted to fit
in the aperture of the alignment member and the lens; and placing
the aligning tool in the apertures of the alignment member and the
focusing lens so as to align the apertures and placing a shim
between the alignment member and the lens so as to provide a
selected distance therebetween; and glass beading the
field-emitting cathode assembly and the lens.
6. The method of claim 5 wherein the alignment member is a can, the
can further comprising wings attached thereto to produce the
selected diameter.
Description
RELATED REFERENCES
[0001] This application is a divisional of application Ser. No.
09/493,379, filed Jan. 28, 2000.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention pertains to electron guns for devices such as
cathode ray tubes (CRTs). More particularly, a package structure
for mounting a field-emitting device into an electron gun is
provided.
[0004] 2. Description of Related Art
[0005] A cathode ray tube (CRT) and other devices requiring an
electron beam normally include an electron gun having a thermionic
emitter as the cathode. The electron gun is assembled to include
the cathode and other electrodes that focus and accelerate the
electron beam. Such electron guns are typically assembled manually
and the cathode is inserted after the gun is assembled. Such
assembly can be costly. It would be an advantage to include the
cathode portion of the gun in the initial assembly.
[0006] The technology to allow replacement of cathodes based on
thermionic emission with cold cathodes based on field emission of
electrons has been developing in recent years. The field emission
of electrons occurs from microtips that are fabricated from
molybdenum, silicon or, in very recent years, carbon-based
materials. It has been demonstrated that the carbon-based material
or diamond-like material can be monolithically integrated with
gated electrodes in a self-aligned structure, using integrated
circuit fabrication techniques ("Advanced CVD Diamond Microtip
Devices for Extreme Applications," MAT. RES. SOC. SYMP. PROC., Vol.
509 (1998)). The use of field emission devices with the extraction
gate built-in eliminates the need for two of the electrodes in an
electron gun built on thermionic emission. Elimination of these
components simplifies the gun and also reduces its length. The
application of the integrated carbon-like cathode and electrodes
into an electron gun has been described in pending and commonly
assigned patent application entitled "Compact Field Emission
Electron Gun and Focus Lens," filed Jul. 19, 1999, Ser. No.
09/356,851, with named inventors Rich Gorski and Keith D. Jamison,
which is incorporated herein by reference.
[0007] Devices heretofore known for assembling cathode structures
and electron guns using field emission cathodes are described in
U.S. Pat. No. 5,898,262. This patent describes a way for packaging
a field-emitting device to construct a color cathode ray tube. An
insulating piece with an indentation for a single field emitting
device that has three emission areas is provided. U.S. Pat. No.
5,869,924 provides an insulating material (plastic) that is created
by filling in an external case, with pins extending through the
insulating material. The cathode device is wire-bonded directly to
the head of the pins. U.S. Pat. No. 5,905,332 discloses additional
portions of an electron gun beyond the field-emitting cathode
itself. The aperture spacing in the focusing portion of the gun is
larger than the spacing between the field emitting devices.
[0008] The cathode, accelerating and focusing elements of electron
guns may be assembled by alignment with a centering tool, spaced
apart with shims and held in place by a nonconductive ceramic that
is sintered onto the outer edge of the elements. This sintering of
the elements to a ceramic structure is called a "glass beading
operation." The shim spacers are then removed to provide the
electrically isolated elements of the electron gun. When thermionic
emitters are used, a barium coated cathode is separately placed
into the gun after this assembly operation. This is necessary
because the fragile barium coating is not able to withstand the
high temperatures at atmospheric pressure required in the glass
beading operation.
[0009] One of the advantages of a field emission electron source is
that the robustness of the cathode can allow the electron gun to be
fully assembled before the glass beading operation. This eliminates
the secondary step of inserting the thermionic component after the
gun is assembled. A packaging technique is needed that takes
advantage of the fact that the field-emission cathode can be placed
at high temperature at atmospheric pressure without damage. The
packaging should lower assembly costs of electron guns based on
field emission cathodes. The package must also be constructed to
allow precise alignment of the cathode in the electron gun. The
structure resulting also should allow the use of the electron gun
in a wide range of CRT neck-diameters.
BRIEF SUMMARY OF THE INVENTION
[0010] An electron gun cathode assembly having a field-emitting
cathode and a method for assembling are provided. The
field-emitting cathode may be carbon-based. A non-conductive
substrate, normally a ceramic material in the form of a disk, has
electrical connection such as provided by a die region to the back
of a field-emitter die. An emitting array has been grown on the die
by known methods. Three field-emitting dies may be spaced on the
substrate to form an electron gun for a color CRT. Electrical
connections for the die and for electrodes integral with the
cathode are made to conductive traces that are connected to pins
that pass through the substrate. A disk or can having one or more
apertures is spaced apart from the emitting array by a separate
spacer ring or the spacing may be created by forming the disk or
can. Normally the substrate, spacer and disk or can are joined by
welding or brazing, by adhesive or mechanically. The cathode
assembly, including the disk or can and spacer, can be aligned and
also aligned with a separate focusing electrode with an aligning
tool that fits in apertures in the disk or can and lens. The entire
assembly can then be glass beaded using known techniques.
DESCRIPTION OF THE DRAWINGS
[0011] For a more complete understanding of the present invention
and the advantages thereof, reference is now made to the following
description taken in conjunction with the accompanying drawings in
which like reference numbers indicate like features and
wherein:
[0012] FIG. 1a shows a cross-section view of one embodiment of a
cathode structure for an electron gun.
[0013] FIG. 1b shows a cross-section view of a second embodiment of
a cathode structure for an electron gun.
[0014] FIG. 1c shows a cross-section view of a third embodiment of
a cathode structure for an electron gun.
[0015] FIG. 2 shows a cross-section view of a fourth embodiment of
a cathode structure for an electron gun.
[0016] FIG. 3 shows an aligning tool being used for alignment of a
cathode structure and an electrode.
[0017] FIG. 4 shows glass beading of a cathode structure and an
electrode.
[0018] FIG. 5 shows a top view of the single cathode and electrical
connections on a substrate that is shown in cross-section in FIG.
1a, but with the top disk removed.
[0019] FIG. 6 shows a top view of three cathodes and electrical
connections on a substrate.
[0020] FIG. 7 shows a top view of one embodiment of an alignment
disk for a three-cathode structure.
[0021] FIG. 8 shows a cross-section view of one embodiment of the
three-cathode structure shown in FIG. 7.
DETAILED DESCRIPTION OF THE INVENTION
[0022] Referring to FIG. 1a, one embodiment of an electron gun
cathode assembly is generally shown at 10. Ceramic substrate 12
supports a field emitting device, which includes die 13 on which
field emitting array 14 has been formed. Array 14 has been formed
using methods for forming field emitting arrays such as disclosed
in Ser. No. 09/169,909, filed Oct. 12, 1998 and commonly assigned,
or Ser. No. 09/169,908, filed Oct. 12, 1998, and commonly assigned,
or other field emitting devices which are known in the art and
disclosed, for example in U.S. Pat. No. 5,869,924, all of which are
incorporated by reference herein. Die 13 may be accurately placed
on substrate 12 at a selected position using fiducials. Electrical
connector 16, which may be a conductive trace made by well known
techniques, connects field emitting die 13 to pin 26.
High-temperature adhesive layer 17 enables a conductive path to the
backside of die 13. The adhesive used to form adhesive layer 17 may
be, for example, Ablebond 71-1 or Ablebond 2106. Conductive trace
18 connects to a bond pad to which wire 20 is attached. Wire 20
connects to an extraction electrode in emitting array 14. Array 14
may also include focus electrodes integrally formed in the array,
as disclosed in the applications and patents cited above in this
paragraph. The electrodes may be electrically connected to
conductive pads on ceramic substrate 12 using a wire bonding
process well known in industry. Ring 22 is a spacer between
alignment disk 24 and ceramic substrate 12 Ring 22 may be metal or
ceramic. The thickness of ring 22 is selected to place aperture 25
in disk 24 at a distance from array 14 so as to focus an electron
beam emanating from array 14 by applying a selected voltage to disk
24. This distance is generally in the range from about 0.1 mm to
about 10 mm. The aperture 25 in disk 24 is aligned with array 14
and disk 24 may be attached to the ring 22 through a weld or braze.
Ring 22 may be attached to ceramic substrate 12 by brazing to
metallized trace 32 on substrate 12. Metallized trace 32 is
electrically connected to pin 21 through via 28. Alignment disk 24
is extremely important since it primarily is used for insuring that
field emitting array 14 is properly centered with other elements of
an electron gun. The outer edge of the alignment disk is used for
mounting the cathode in an electron gun, as discussed below.
Electrical connection to disk 24 through pin 21 allows disk 24 to
be used as a focus lens in an electron gun. The diameter of
alignment disk 24 may be sized for placement in a wide range of
sizes of CRTs or other devices. Disk 24 is typically formed from
stainless steel. Conductive trace 16 is connected to pin 28. Pins
such as 26 and 28 may be formed from iron or copper-based alloys,
for example. Contact wires (not shown) may be spot welded to the
pins during the final stemming operation. The wires provide
electrical connection outside of the CRT.
[0023] A second embodiment of an electron gun cathode assembly is
shown generally at 11 in FIG. 1b. This embodiment is similar to
that in FIG. 1a, with the spacing ring 22 removed. In this
embodiment, the alignment disk is formed with cylindrical side 9 to
enable the required spacing between the alignment disk and field
emitting die. The alignment disk may be mechanically and
electrically attached to metallized trace 32 on the substrate with
either a weld or an adhesive bond. Metallized trace 32 is
electrically connected to pin 21. This embodiment may be more
cost-efficient since it eliminates the need to manufacture spacing
ring 22.
[0024] A third embodiment of an electron gun cathode assembly is
shown generally at 45 in FIG. 1c. This embodiment is similar to 1a,
however it instead allows for a cathode connection to die 13
through wire 46 to metallized trace 16 that is connected to pin 26.
This is the preferred embodiment in those instances in which the
backside of die 13 is not conductive.
[0025] A fourth embodiment of an electron gun cathode assembly is
shown generally at 30 in FIG. 2. In this embodiment,
cylinder-shaped can 34 having wings 36 is used for insuring that
field emitting array 14 is properly centered with other elements of
an electron gun and for mounting the cathode in an electron gun.
The diameter of can 34 or the dimensions of wings 36 may be
selected to allow placement of assembly 30 in a wide range of sizes
of CRTs or other devices. Ring 22 is inserted in can 34 and acts as
a spacer to provide the optimal separation between emitting array
14 and aperture 25 in can 34. Ring 35 is inserted after the cathode
assembly and is used to lock the cathode in place. Braze 29 may be
used to fasten pins into ceramic substrate 12. Can 24 is typically
formed of stainless steel. One advantage of the cylinder-shape can
is that easier mechanical alignment is attained by tightly fitting
substrate 12 into the opening in can 34. Another advantage is that
this package assembly allows the additional option of glass bead
attaching the can 34 to the other elements of the electron gun
prior to insertion of the cathode assembly.
[0026] FIGS. 3 and 4 show how electron gun cathode assembly 30 may
be aligned with other electrodes in a CRT or other device and glass
beaded into place (cathode assemblies 10, 11, and 45 would be
assembled in similar manner). Aligning tool 38, sized to fit into
aperture 25 of gun 30 and into the aperture of focusing lens 39 or
any other grids to be placed in the device, is placed in the
apertures and aligned along the axis of the device. Spacing between
the gun elements may be achieved with the use of temporary shims 47
that are later removed. Gun 30 and other lenses or grids are then
fixed in place using ceramic 40 (FIG. 4). Aligning tool 38 and shim
47 are then removed. Alternatively, gun 10 or 11, for example, may
be assembled in place of gun 30 using the same procedure.
[0027] Referring to FIG. 5, a top view is shown of the cathode
assembly shown in cross-section in FIG. 1a but with disk 24
removed. Ceramic substrate 12, field emitting die 13 and field
emitting array 14 are shown from the top. Field emitting die 13 is
bonded to die flag region 42 with conductive cement, as disclosed
above. The electrically conductive adhesive enables a conductive
path to the back side of field emitting array 14. Die flag region
42 may be formed on ceramic substrate 12 by a metal, typically
tungsten, although copper or other metals would be satisfactory.
The metal is typically screened on and fired with the ceramic. The
ceramic is typically aluminum oxide, although other ceramics would
be satisfactory. Such ceramic substrates are available from
Kyocera, Coors or other suppliers. Wire bond pads 44 provide a
terminal for fixing wire bond connections between elements of the
electron gun and pins such as 26 and 27. Wire leads such as 20 of
FIG. 1 are typically joined to wire bond pads by thermosonic
bonding, using techniques well known in industry. If in integral
focus electrode is present in array 14 a separate wire lead is
connected to the focus electrode and to a pad such as 44.
Conductive traces such as 16 and 18 electrically connect pins to
various components of the electron gun or to the die flag region.
Spacer ring 22 was discussed above. It may be formed from KOVAR, a
steel alloy or may be eliminated and the alignment plate formed to
create the required spacing as in FIG. 1b. A single field emission
array is illustrated in FIG. 5, which would be used in a CRT for a
monochrome gun.
[0028] FIG. 6 illustrates one embodiment of an assembly of three
emission arrays to be used in an electron gun to be placed in a
color CRT. In this case, one die is needed for red, one for green,
and one for blue. All three dies 14 are mounted on die flag region
42. Additional pins will be connected through conductive traces
such as 18 to wire bond pads such as 44. Die flag region 42 is used
for connecting through field emission dies as described above. With
three emission areas, a disk such as disk 24 of FIG. 1a or a can
such as can 34 of FIG. 2 would have three openings, each to be
placed opposite arrays 14. The disk or can may then be fixed to
ring 22.
[0029] Referring to FIG. 7, alignment disk 50 to be used in another
embodiment of a packaging device including three emission arrays is
illustrated. Disk 50 serves the same purpose as alignment disk 24
of FIG. 1a or FIG. 1b. The disc includes three apertures 52. Also
shown are three formed impression areas 54 that may be used to
provide the correct spacing of the aperture to the field emitting
array 14 of FIG. 6. Each cathode assembly, including field emitting
array 14 would be centered under aperture 52. Alternatively, the
impression areas may not be present and ring 22 of FIG. 5 may be
joined by welding or cementing to alignment disk 50. A side view of
the same assembly is shown in FIG. 8. Disk 50 may be glass beaded
into an electron gun package using techniques described above
whereby at least one aperture in the disk may be used for
alignment.
[0030] The foregoing disclosure and description of the invention
are illustrative and explanatory thereof, and various changes in
the details of the illustrated apparatus and construction and
method of operation and assembly may be made without departing from
the spirit of the invention.
* * * * *